Chiu S W, Clark M, Balaji V, Subramaniam S, Scott H L, Jakobsson E
National Center for Supercomputing Applications, University of Illinois, Urbana 61801, USA.
Biophys J. 1995 Oct;69(4):1230-45. doi: 10.1016/S0006-3495(95)80005-6.
In this paper we report on the molecular dynamics simulation of a fluid phase hydrated dimyristoylphosphatidylcholine bilayer. The initial configuration of the lipid was the x-ray crystal structure. A distinctive feature of this simulation is that, upon heating the system, the fluid phase emerged from parameters, initial conditions, and boundary conditions determined independently of the collective properties of the fluid phase. The initial conditions did not include chain disorder characteristic of the fluid phase. The partial charges on the lipids were determined by ab initio self-consistent field calculations and required no adjustment to produce a fluid phase. The boundary conditions were constant pressure and temperature. Thus the membrane was not explicitly required to assume an area/phospholipid molecule thought to be characteristic of the fluid phase, as is the case in constant volume simulations. Normal to the membrane plane, the pressure was 1 atmosphere, corresponding to the normal laboratory situation. Parallel to the membrane plane a negative pressure of -100 atmospheres was applied, derived from the measured surface tension of a monolayer at an air-water interface. The measured features of the computed membrane are generally in close agreement with experiment. Our results confirm the concept that, for appropriately matched temperature and surface pressure, a monolayer is a close approximation to one-half of a bilayer. Our results suggest that the surface area per phospholipid molecule for fluid phosphatidylcholine bilayer membranes is smaller than has generally been assumed in computational studies at constant volume. Our results confirm that the basis of the measured dipole potential is primarily water orientations and also suggest the presence of potential barriers for the movement of positive charges across the water-headgroup interfacial region of the phospholipid.
在本文中，我们报道了液相水合二肉豆蔻酰磷脂酰胆碱双层膜的分子动力学模拟。脂质的初始构型为X射线晶体结构。该模拟的一个显著特点是，在加热系统时，液相是从独立于液相集体性质确定的参数、初始条件和边界条件中出现的。初始条件不包括液相特有的链无序。脂质上的部分电荷通过从头算自洽场计算确定，无需调整即可产生液相。边界条件为恒压和恒温。因此，与恒容模拟不同，膜不需要明确假设具有被认为是液相特征的面积/磷脂分子。垂直于膜平面，压力为1个大气压，这与正常实验室情况相对应。平行于膜平面，施加了-100个大气压的负压，该负压源自空气-水界面处单层的测量表面张力。计算得到的膜的测量特征通常与实验结果非常吻合。我们的结果证实了这样一个概念，即对于适当匹配的温度和表面压力，单层是双层的一半的近似。我们的结果表明，流体磷脂酰胆碱双层膜中每个磷脂分子的表面积比恒容计算研究中通常假设的要小。我们的结果证实，测量到的偶极势的基础主要是水的取向，并且还表明在磷脂的水头界面区域存在正电荷移动的势垒。
